Gel composition and its use as a braking medium

ABSTRACT

A gel composition is provided which on a weight basis consists essentially of 94.0 to 94.4 percent water, 5.50 t0 5.75 percent fumed silica, 0.025 to 0.035 percent of a fatty diamine and 0.002 to 0.004 percent of an ethylene oxide polymer. The composition is particularly useful as a braking medium in a method for stopping high speed monorail sleds employed in aerospace research.

United States Patent Brown Nov. 28, 1972 [5 GEL COL [POSITION AND ITS USE AS A [56] References Cited BRAKING MEDIUM UNITED STATES PATENTS [721 lnvenm Bmw, Am 2,844,220 7/1958 Muehlner .,..l88/38 73 ASsig-nee: The United States of Anwrica 8 3,390,743 7/1968 ..188/38 ted b t Secretary f the jig g2 y he 0 Primary ExaminerDuane A. Reger Attorney-Harry A. Herbert, Jr. and Cedric H. Kuhn [22] Filed: Feb. 16, 1971 21 Appl. No.: 115,742 [57] ABSIRACT A gel composition is provided which on a weight basis consists essentially of 94.0 to 94.4 percent water, 5.50 [52] US. Cl ..188/33, ,188/38 o 5 75 percent f m d Silica, 0 025 to 0035 percent [51] Int. Cl. ..B6lh 9/00 of a fatty diamine and 0.002 to 0.004 percent of an [58] Field of Search ..l88/2 R, 5, 6, 32, 33, 38, ethylene oxide polymer. The composition is particu- 1 3 5 40, 41 larly useful as a braking medium in a method for stopping high speed monorail sleds employed in aerospace research,

3 Claim, No Drawings GEL COMPOSITION AND ITS USE AS A BRAKING MEDIUM FIELD OF THE INVENTION This invention relates to a gel composition particularly adapted for use as a braking medium. In one aspect it relates to a method for stopping high speed rail vehicles.

BACKGROUND OF THE INVENTION In aerospace research various tests are conducted that utilize high speed vehicles. I The vehicles are generally referred to as sleds or monorail sleds since they usually run on a single railroad-type rail. However, unlike railroad cars which run on wheels, sleds are held in position on the rail by metal slippers, usually two in number, attached to a sleds underside. The slippers comprise a flat plate member having a width such that it can ride on the head of the rail. Extending downwardly from each side of the plate member is a lip which curves inwardly underneath the head of the rail. The inwardly extending edge of the lip is spaced apart from the webof the rail. When the sled is at rest, there is a small space, e.g., /a to M1 inch, between the lower surface of the rail head and the upper surface of the inwardly extending portion of the lip. At relatively low speeds, e.g., at about 400 to 500 feet per second, the sled rides on the flat plate members of the slippers. However, as the velocity increases the sled rises so that it actually rides on the upper surface of the inwardly extending portions of the lips that bear against the lower surface of the rail head. The sleds are rocket propelled, generally utilizing a solid propellant although liquid propellants are sometimes used.

A major problem in the use of high speed sleds is their recovery in an undamaged condition. The-sleds carry sophisticated test items and instruments which are ruined when the sleds run off the end of the track. In addition to being expensive, this prevents a visual inspection of the test items after completion of the runs. Various methods for stopping the sleds have been suggested and tried, but each method has disadvantages rendering it unsatisfactory. In one method elongated plastic bags were filled with water and placed on the track. The manpower requirements to fill and install the bags and then clean up after the tests were excessive. On vehicle entry the plastic bags became lodged between the vehicle and rail, placing an undue stress on the sled slippers. Another method involved the placement of Styrofoam water trays on the rail. However, the cost of the trays is very high, and many manhours of work were required to clean the area of small pieces of styrofoam. Furthermore, in neither of these methods was it possible to program the height of the bags or trays, e. g., from Va inch to 4 inches, for high speed vehicle recovery.

It is an object of this invention, therefore, to provide a braking medium for use in the recovery of high speed monorail sleds.

Another object of the invention is to provide a gel composition which contains a very high percentage of water.

A further object of the invention is to provide a gel composition which is non-corrosive and which is not strongly adherent to metal.

Still another object of the invention is to provide a method of stopping high speed monorail sleds.

Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.

SUNIMARY OF THE INVENTION This invention in one embodiment resides in a gel composition which, on a weight basis, consists essentially of 94.0 to 94.4 percent water, 5.50 to 5.75 percent fumed silica, 0.025 to 0.035 percent N-oleyl propylene diamine, and 0.002 to 0.004 percent of an ethylene oxide polymer having a molecular weight of about 600,000. It is within the contemplation of the invention to replace a portion of the water with an equal part by weight of an alcohol, such as ethlene glycol, if the composition is to be subjected to freezing temperatures. The substitution of up to about 10 weight of the water with an alcohol is usually sufficient. It has been found that the indicated amounts of the ingredients in the composition are critical in providing a gel that functions satisfactorily as a braking medium. For example, any substantial deviation from the amounts will result in a composition that iseither too thin or too thick and gummy.

In another embodiment, the invention resides in a method for stopping high speed sleds which run on a rail. The method comprises the steps of applying a coating of the above-described gel composition to the top surface of the head of the rail; propelling the sled at a high speed on an uncoated portion of the rail toward the coated portion of the rail; and contacting the sled with the gel composition, thereby dissipating the composition and reducing the speed of the sled until it comes to a stop. The term dissipating is used herein to indicate that the gel composition is broken down. In other words, the water is knocked out of the composi tion, the impact of the sled causing the water and other components to be sprayed outwardly along the sides of the rail.

In preparing the gel composition of this invention, tap water can be used. However, the pH of the water should be in the range of about 6.4 to 7.9.

The fumed silica is a very pure silica which on a dry basis is 99 percent silicon dioxide. It is in the form of very fine particles having a particle size of about 0.007 to 0.012 micron and a surface area of 175 to 350 tn lg. The silica is produced by the hydrolysis of silicon tetrachloride at 1 100 C. As the material is produced at a high flame temperature, it is generally classified as a fumed silica.

The fatty diamine employed is N-oleyl propylene diamine. The diamine induces an increase in viscosity or functions as a gelling agent. While other fatty diamines have been tried in preparing the gel composition, it has been found that N-oleyl propylene diamine is the only one that provides a composition having the desired viscosity.

The polymer of ethylene oxide used has a molecular weight of about 600,000. This material appears to function as a lubricant. Thus, its presence facilitates the removal of the gel composition from the mixing apparatus in which it is prepared. Furthermore, the gel composition is readily extrudable because of the inclusion of the ethylene oxide polymer, thereby making it easy to apply the composition to a rail.

The gel composition is prepared by initially adding the water to a vessel provided with a mixing paddle. It

has also been found that an ordinary cement mixer can be advantageously employed in the mixing operation. The fumed silica is then introduced slowly into the water while slowly stirring or agitating the mixture. After the fumed silica has been thoroughly dispersed in the water, the fatty diamine is slowly added with continued stirring. Thereafter, the ethylene polymer is added. The gel composition begins to form as soon as the fatty diamine is charged while stirring is continued until a homogeneous composition is formed. The time required will depend upon the size of the batch being prepared. For example, in formulating 60 gallons of the composition, the, maximum mixing time is about 8 minutes.

If requiredto prevent freezing, an equal amount by weight of an alcohol may be substituted for the water. The gel composition is milky white in color. If desired, the composition can be colored by the addition of standard food colors without adversely affecting its properties.

As mentioned hereinbefore, the gel composition of this invention contains 94 to 94.4 percent water. The amount of water is so great that the composition might well be denoted as congealed water. It is important that the gel contains this large amount of water since its presence makes possible the exchange in momentum that occurs in carrying out the method of this invention. Another important property of the composition is its ability to retail 90 percent of its extruded shape for at least 3 hours. Furthermore, the gel can withstand a wide range of temperatures, e.g., from 20to 130 F., without freezing and with only a small amount of evaporation, e.g., less than 10 weight percent during a 3 hour period. Still further, the gel composition is nonadhesive in nature when in contact with a metal. As a result, the gel is readily dissipated when contacted with a high velocity sled and does not stick to the rail. Another important property of the gel composition is that it is non-corrosive. Thus, damage to a rail through corrosion does not occur as a result of application of the gel on the rail.

The gel composition can be applied to the rail by any suitable means. For example, it can be applied by hand by merely troweling the gel onto the top surface of the head of the rail. Forms, vertically positioned against the side of the rail and extending above the aforementioned top surface to form a trough, can be utilized with advantage when using this method of application. Since the gel composition is readily extruded, it is usually preferred to apply the gel by an extrusion means. For example, an extruder comprising a cylinder fitted with a piston and having an inlet for filling and an outlet in the form of a spreader can be employed. The gel composition is applied to the top surface of the head of the rail in varying thicknesses that increase in the direction of travel of the sled. For example, the initial layer may be /4 inch thick for a specified distance with subsequent layers increasing in increments, for example, of V4, is or 1 inch. A maximum layer thickness of 4 inches has generally been found to be sufficient. The high speed of the vehicle is reduced until it becomes zero as a result of momentum exchange which is a function of the direct braking force exerted by the braking medium, i.e., the gel composition. Since it is desired that the exchange of momentum be on a graduated basis in order to avoid any abrupt change in velocity that might place an undue stress on the sled, the thickness of the layers of braking medium are varied as indicated above. The momentum of a sled is directly related to its weight and velocity, and the exchange of momentum will also depend upon the configuration of the front portion or nose of the sled that contacts the braking medium. Thus, the length of the various layers vary with the type of sled and the speed at which the sled contacts the braking medium. However, one skilled in the art of fluid dynamics can readily determine the EXAMPLE I A gel composition was prepared, utilizing the following formulation:

Weight percent Water 94.305 Cab-O-Sil (M-S) 5.660 Adogen 572 0.032 Polyox WSR-ZOS 0.003 100.000

(1)Afumedsilicahavingasurface areaof200i25 m lgmandaparticle size of 0.0l2 micron, a product of Cabot Corporation, Boston, Mass.

(2) N-oleyl propylene diamine, a product of A.D.M. Chemicals, Minneapolis, Minn.

(3) An ethylene oxide polymer having a molecular weight of 600,000, a product of Union Carbide Corp., New York, N. Y.

The gel was prepared by slowly adding the Cab0-Sil fumed silica to the water contained in a mixing vessel. After the silica was thoroughly dispersed in the water,

the Adogen fatty diamine was slowly introduced with stirring. The gel composition began to form upon introduction of the diamine. Thereafter, the Polyox ethylene oxide polymer was added while continuing the stirring. After about 8 minutes a homogeneous gel composition was formed that had a viscosity of 700,000 centipoises and a specific gravity of 1.008.

The gel composition was applied by means of an extrusion apparatus to the top surface of the head of a monorail having a total length of about 35,000 feet. The gel was applied in thicknesses and for the lengths of rail indicated in Table I.

Table l Thickness, inch Length, feet 500 A sled propelled by a high impulse motor and having as a front end or nose a vertical wedge with an 18 half angle was run on the rail to which the gel had been applied. The bottom edge of the vertical wedge rode about )6 inch above the top surface of the head of the track. The sled entered the braking medium at a Example 11 Samples of the gel composition prepared as in Example I were tested to determine the weight loss at dif-,

ferent temperatures. The tests were conducted in a forced air oven with the samples being placed in a plastic box. The box has a volume of 351.2 cm". and an exposed area of 71.7 cm The volume to surface area ratio of the sample was 4.9. All tests were conducted for a period of 6 hours.

The results of the tests are shown below in Table II.

Table II Temp., F initial wt, gm. wt loss, Loss los/hr gm. 90 374.11 15.41 4.1 0.68 100 370.72 18.70 4.9 0.82 l 10 369.72 23.61 6.4 1.07 120 363.30 29.29 8.4 1.35

In actual use, the same mass of gel has a volume to surface ratio of 2.12. Therefore, the actual evaporation and shrinkage at the indicated temperatures would be 2.31 (4.9 (2.12) times the test values. These value are shown in Table III.

Table III %loss/hr X 2.31

Temp., F. loss/hr loss/3 hrs From the foregoing data, it is seen that the percentage loss in the weight of the gel for a 3 hours period was less than 10 weight percent at the various temperatures.

As will be evident to those skilled in the art, various modifications of this invention can be made or followed in the light of the foregoing disclosure without departing from the spirit or scope of the invention.

1 claim:

1. A method for stopping high speed sleds which run on a rail having a head with a flat top surface which comprises the steps of applying to said top surface a coating of a gel composition consisting essentially of 94.0 to 94.4 weight percent of a mixture of water and an alcohol, the amount of alcohol in said mixture being from 0 to 10 weight percent, 5.50 to 5.75 weight percent fumed silica in finely divided particle form, 0.025 to 0.035 weight percent N-oleyl propylene diamine, and 0.002 to 0.004 weight percent of an ethylene oxide polymer having a molecular weight of about 600,000; propelling the sled at a high speed on an uncoated portion of the rail toward the coated portion of the rail; and contacting the sled with the gel composition, thereby dissipating the compositing and reducing the speed of the sled until it comes to a stop. 2. The method of claim 1 in which the gel composition is applied to said top surface in layers of varying thicknesses that increase in the direction of travel of the sled.

3. The method of claim 1 in which the thickness of the layers of the gel composition vary from one quarter of an inch to 4 inches. 

2. The method of claim 1 in which the gel composition is applied to said top surface in layers of varying thicknesses that increase in the direction of travel of the sled.
 3. The method of claim 1 in which the thickness of the layers of the gel composition vary from one quarter of an inch to 4 inches. 